Finding bubbles of various sizes on the aluminum foil surface after sealing is a common issue. This is not just a cosmetic problem but may also compromise the sealing effectiveness. Leadtra Packaging has compiled a guide to help you troubleshoot common causes and find targeted solutions.

1. If Bubbles Are Regular, Check Sealing Parameters First

If bubbles appear in a regular pattern (e.g., fixed positions, consistent sizes), the issue is likely related to sealer parameter settings.

Excessive sealing temperature or uneven pressure can cause localized overheating and deformation of the seal layer, resulting in bubbles upon cooling. As a general reference, try setting the temperature around 180°C, stabilizing pressure at 0.4MPa, and using a sealing time of about 2 seconds. Fine-tune these parameters as needed and test.

2. If Bubbles Are Randomly Distributed, Check Bottle Mouth Cleanliness

If bubble positions are irregular, bottle mouth contamination is the primary suspect. Residual water, oil, or dust on the bottle mouth creates an isolation layer during sealing, preventing the heat-seal layer from fully fusing with the bottle mouth and producing bubbles.

Solution: Ensure the bottle mouth is clean and dry before sealing, using a lint-free cloth if needed; operators should wear clean gloves to avoid contaminating the bottle mouth with grease.

3. If Large Areas Bubble, Check Paperboard Moisture

If you are using non-separating sealing gaskets and bubbles cover a large area, the problem often lies in the paperboard layer. The raw wood pulp inside coated white paperboard readily absorbs moisture. During the instantaneous heating of sealing, this moisture turns to steam. If the paperboard's surface coating is too tight to allow the steam to escape, it can swell the surface layer into bubbles.

Solution: Choose high-quality coated white paperboard whose surface coating has microscopic pores (invisible to the naked eye) to allow steam to escape; or use gaskets that have undergone moisture-removal treatment during production to reduce residual moisture in the paperboard.

4. If Bubbles Have Black Spots, Environmental Dust May Be the Cause

If bubbles contain small black spots at their center, it indicates that dust or other contaminants were present on the film or bottle mouth during sealing. Dust particles lift the aluminum foil layer, creating voids that appear as bubbles with black spots.

Solution: Control workshop cleanliness, pay attention to indoor ventilation and dust removal; inspect the film surface before use to avoid dust adhesion.

5. Summary: Where the Bubbles Are, That‘s Where the Problem Is

Regular bubbles → Start by adjusting sealing parameters (temperature, pressure, time)

Random bubbles → Prioritize checking bottle mouth cleanliness

Large-area bubbles (gasket type) → Check paperboard quality and moisture content

Bubbles with black spots → Pay attention to workshop environment and film cleanliness

Bubbles after sealing are not necessarily a material problem; they often reflect issues with process, environment, or operational details. Once you identify the right direction and make proper adjustments, most problems can be resolved.

For further analysis, you are welcome to send us samples, and Leadtra Packaging will provide targeted recommendations.